Thermal printers can form print images by heating a print medium that is sensitive to heat. In some examples, such print medium (referred to as a “thermal print medium”) can be coated with a thermally sensitive coating. The thermally sensitive coating can change color (e.g., turn from white to black, or change between other combinations of colors) in portions of the thermally sensitive coating that are heated. The portions that change color form a target image on the print medium. The heating can be performed using heating elements arranged on a thermal head of a thermal printer.